Method for treating hydrogels



March 26, 1957 H. A. sHABAKl-:R 2,786,818

METHOD FOR TREATING HYDROGELS Filed Dec. 25, 1952 l @Ar/u yf? Z INVENTORATTORNEY United States Patent O METHOD FOR TREATING HYDROGELS Hubert A.Shabaker, Media, Pa., assigner to Houdry Process Corporation,Wilmington, Del., a corporation of Delaware Application December 23,1952, Serial No. 327,549

4 Claims. (Cl. 252-448) The present invention relates to the manufactureof inorganic oxide gels in the form of spheroidal beads or pellets ofother desired shape, particularly of the type employed as Contact massesin the catalytic conversion of hydrocarbons.

vSuch catalyst beads or pellets are commonly prepared by introducinggelable hydrosol into a water-immiscible liquid wherein the masses ofhydrosol set to form beads or pellets of hydrogel. Immediately uponformation of the hydrogel a transformation begins to take place, as aconsequence of which the gel becomes less hydrous and undergoes variousother changes in its characteristics. Such transformation may occurgradually, simply by letting the hydrogel stand `at room temperature fora substantial period of time, or it may be accelerated by elevating thetemperature. The transformation that takes place during this period iscommonly referred to as aging The matter of aging the beads intheprocess of manufacture is of considerable importance, inasmuch astheproperties and characteristics which render the final product speciallysuitable as a catalytic contact mass depend in large measure uponsuccessful aging. Aging can occur at any time the gel is in a wet state,that is at any time prior to its reaching a state of substantialdryness.

A method for preparing hydrogel beads or pellets of the type referred toherein is disclosed in application, Serial No. 187,500, for Bead FormingProcess, filed September 29, 1950, in the name of Edward H. Lebeis, nowPatent No. 2,665,258. That application discloses a process involving apartial-drying stage, the control of which is of vital importance withrespect to any aging that may occur in'this stage. In the partial-dryingstage the drying is effected lat a constant rate, since the evaporationof water takes place only at the surface of the bead. The drying ratewill remain constant until the plane of vaporization begins to recedeinto the interior of the bead, after which the drying rate will varydirectly with thel moisture content. 1 Major transformations, occuringas a result of aging, vare observed to take place during the preliminaryor early stages of any drying step. For example, the beads shrink to afraction of their original volume and are increased considerably inhardness, while in general still retainin the shape :assumed duringtheir formation. j 'Aging vof the hydrogel fixes the density of thefinal product, the iinal density being in general an inverse function ofaging. That is, the more drastic the aging, the lower the final beaddensity. In addition to the extent of aging, the uniformity of aging isof considerable importance; 'Non-uniform aging may produce beads of'widely different' densities,` with substantial variation in physicalstructure, which is undesirable from the standpoint of,` physical andcatalytic considerations.

It has been found that for optimum conditioning of the beads partialdrying should be stopped while the beads are still in the constant-ratedrying period, and .Whliertbe :water contentifroin bead to..bead is asnearly ice uniform as possible. Also, that careful handling of the beadsin the partial drying apparatus is necessary, because the freshlyprepared beads are weak and are subject to breakage as a result ofcrushing, or of bouncing when permitted to fall freely.

In my copending application for Method and Apparatus for DryingHydrogels, filed concurrently herewith as application, Serial No.327,550, now Patent No. 2,717,458, I have disclosed an improved methodand apparatus for effecting the constant-rate drying of freshly preparedhydrogel beads. The drier illustrated therein as an embodiment of theinvention provides cross-flow drying over the exposed surfaces ofcontinuously moving, shallow compact masses of beads, with frequentmixing of the beads. Such continuous movement of the beads is effectedby passing them downwardly as a nested plurality of confined Zig-zagstreams, Withmixing of the beads at the ends of each sloping run of thezig-zag paths. The partially dried beads vare discharged downwardly asan elongated compact moving column from each path of the drier. Thereare no moving parts of the drier contacting the beads at any time, andthe beads are not permitted to fall freely during any portion of theirdescent through the drier.

The present invention is particularly concerned with such aging of thebeads as may occur subsequent to the partial-drying operation, that is,the operation in the manufacturing process wherein the beads areundergoing constant-rate drying.

In accordance with the present invention hydrogel beads or pellets whichhave been partially dried in a constant-rate drier, with consequentpartial aging, are immediately thereafter further aged to a desireddegree of completion by being passed directly from the constantratepartial-drying zone to and through an aging zone wherein Vthe beads aremaintained at substantially the same conditions of temperature andhumidity as existed at the time of their withdrawal from the partialdrying zone. Within the aging zone the temperature and the equilibriummoisture content of the beads is maintained substantially constant for atime suiiicient to effectthe desired additional aging, which additionalaging is carried out without additional drying, that is, in the absenceof drying gas. The time of residence of the beadswithin the aging zoneis controlled by varying the volume or capacity of the aging zone,thereby permitting the rate of flow of the beads through both thepartial drying zone 4and the aging zone to be maintained constant andcontrollable by varying the rate of withdrawal from the aging zone.

In accordance with a preferred embodiment of the invention, hydrogelbeads which have been passed downwardlythrough a drier, in which thebeads are repeatedly mixed while being contacted with a current of hotdrying gas to effect a partial drying of the beads, are withdrawntherefrom through an elongated draw-off leg comprising telescopingconduit sections adjustably connected to provide a confined draw-offpath of variable volume, so that the residence time of the beads thereinmay be controlled at will by adjustment of the volume. An adjustablevalve at the bottom of the draw-off leg controls the rate of ilow of thebeads through the aging zone and the drier, In order to maintain thebeads Within the draw-off leg in substantially the same condition asthey were when they left the drying zone, the draw-off leg is providedwith heatingelement, such `as a steam jacket or other suitable means,for maintaining the temperature of 4the beads within the draw-olf leg atany desired level.

For a fuller understanding of the invention reference may be had to thefollowing description and claims, taken in connection with theaccompanying drawing forming a-part of this application, in which thesingle ligure of the drawing shows a diagrammatical representation of adrier adapted to elfect a constant-rate partial drying of the beads,associated with an adjustable draw-off leg comprising an aging zonewherein the desired aging of the beads is carried to the desired degreeofcompletion under controlled conditions of temperature and humidity.

Referring to the drawing, the numeral'l represents a drier, which may beof the type illustrated and described in my aforesaid copendingapplication, Serial No. 327,550, filed December 2-3, 1952, now Pat-entNo. 2,717,458, or which may be of any other type suitable to effect auniform partial drying of the beads. While my copending applicationVshows a drier adapted to handle a plurality of separate gravitatingcatalyst streams, each provided with its own draw-off leg, for thepurpose of simplification the illustrated embodiment of the presentinvention is shown with but one draw-off leg, it being understood thatmore than one may be provided or that Vthe several streams within thedrier may be combined upon withdrawal to' discharge as a single compactmoving column.

The hydrogel beads, which may be silica-alumina beads, are introducedinto the upper end of drier 1 through an inlet conduit 2 connected to ahopper or other means for supplyingnewly-formed hydrogel beads whichhave set suicie'ntly' to permit their being handled in the drier withoutexcessive breakage.

Drying gas at elevated temperature is supplied through inlet conduit 3to th'e lower end of the drier 1 and, together with the moisture removedfrom' the beads, is discharged from the upper end of the drier throughoutlet conduit 4. It is to be understood, of course, that thel inventionis not limited to any particular manner of introducing and removing thedrying gas, or of contacting the beads with the' drying gas within thedrier. Preferablyf however, the drier is of a ty'pe in which the beadsare conveyed in shallow-bed formation, with frequent mixing of thebeads, while the drying' gas is directedv over the exposedl surfaces ofthe beads. Since the drier per s'e forms no part of this invention,description vand illustration of the internal structure of the drier isnot considered essential for an understanding of the invention, and istherefore omitted. It suflices to say that the beads reach the lowermostregion of drier 1 in a partially` dry state, drying having been carriedo ut nearly to completion of the constant-traite drying'period.Typically the beads may be at a temperature of about 150-200 F. and at amoisture content of about 75-3'00 wt. percent on the washed dry basis.

The beads are withdrawn from the drying zone of chamber 1 before bothaging and constant-rate drying have been completed. The beads passdownwardly as a compact moving column through a draw-off leg comprisingan upper vertical tubular conduit S, having its upper end adapted toreceive the beads from the lower region of the drying chamber, and alower tubular vconduit 6 telescopic'ally receiving within its upper endthe lower' end of conduit 5 and being longitudinally adjustable inrelation thereto so as to provide a variable volume for thel draw-olfleg as a whole. t l

The draw-off leg is provided with a suitable valve 7 at its' lower endin order to control the rate of catalyst flow through the drier. Afterdischarging through valve 7 the partially dried, aged catalyst isconveyed, as by conduit 8,- to the next stage in the process ofmanufacture, which may, for example, be a base exchange and washingstep, preliminary to nal drying and heat treating.

As the catalyst descends within the' draw-olf leg, or final aging zone,its temperature is maintained substantially constant by indirect heatexchange with a tluid,'such s steam, circulating through a cylindricaljacket member 9 surrounding the draw-on leg. The heat exchange uid issupplied to the jacket chamber 10 through inlet line-11, andisdischargedfrom the chamber through outlet line- 12.

VBy my invention I am enabled to partially dry the 4. hydrogel beadsalmost to completion of their constantrate drying period and to deliverthe beads, without substantial change in the degree of dryness or in thetemperature attained in achieving such degree of dryness, to an agingzone through which the beads are passed without substantial change ofeither temperature or `degree of dryness until the desired arrint ofaging is completed. The method of my invention has the advantage ofenabling the beads to be aged to the desired degree of completion aftertheir removal from the drying zone, without the need for reheating thebeads and without the danger of condensation of steam on them.

Example l Silica-alumina hydrogel beads are prepared as follows: streamsof commercial water glass (N-Brand sodium silicate) are admixed withaluminum sulfate and sulfuric acid in a rotating, jet-type mixing headto give a pH of 8.5 and a weight ratio of 93 silica to 7 alumina, theproduct concentration being grams of SiOz plus A1203 per liter of totalsolution. The resulting hydrosolis discharged into a bath of lightmachine oil wherein the hydrosol stream forms into and sets as hydrogelglobules. The formed globules or beads are picked up below the oil bathby a conveying stream of dilute aqueous sodium sulfate (5% Na2SO4) anddischarged onto a screen to remove the conveying liquid.

The hydrogel beads, thus freed of liquid, are theny subjectedto partialdrying by continuous passage through a drier for 12 minutes operating at200 F. dry bulb--140 F. wet bulb temperature-whereby the moisturecontent of the beads is reduced to approximately 200% `by weight C. drybasis).

The thus partially-dried beads are continuously discharged from thepartial drying zone into anaging zone therebelow, arranged to pass thebeads through at a rate which will give a residence time of 1 hour. Theaging zone is maintained at a temperature of 138 F.

The hydrogel beads, partially dried and aged in accordance with theinvention as described above, are then subjected to further conditioningtreatment to produce the nal product. The aged beads, upon removal fromthe' aging zone, are cooled carefully, then subjected to washing andbase exchange followed by final washing, and then subjected t'o finaldrying by conventional drying means. Such further treatment maycomprise, for example, iive l-hour distilled water washes, then tive2-'hour aluminum sulphate solution treatments, followed by twenty l-hourwater washes to remove the sulphate. Final drying may then be elected bysubjecting the beads to a temperature of 250 F. dry bulb-212 F. wet bulbfor a period of 1V: hours.

While, for the purpose of illustration, I have shown the desired agingas being accomplished in a telescoping tubular draw-oir leg of variablevolume, it will be apparent to those skilled in the art that such agingmay be' carried out in a chamber of any desired configuration, providedsubstantial uniformity of solids flow and uniformity of temperature andmoisture conditions are assured throughout the horizontalcross-sectional area of the aging zone or chamber. Furthermore, it iscontemplated that other suitable means for providing a variable volumeof beads in the draw-off leg may be used. For example, instead oftelescoping the separate sections of the draw-off leg, differentdischarge levels may be provided at the lower end portion thereof.

Obviously many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such lnlita-tions should be imposed asare indicated in the appended claims. Y

What is claimed is:

l. In a continudus process for treating preformed particles of.silica-alumina hydrogel having a moisture content up to about 300% byweight to condition the same for use as a contact material, theimprovement which comprises introducing the wet liydrogel particles intoa ilowing stream of drying gas having a temperature of about 150 to 200F. for a time suicient to reduce the moisture con- V tent of saidparticles to about 200%, passing the partially dried hydrogel particlesthrough an aging zone maintained at about 138 F. during a time intervalof about one hour, and then washing and drying the aged particles.

2. A process as defined in claim l in which the partial drying of saidhydrogel particles form a moisture content of up to about 300% to amoisture content of about 200% is effected by subjecting said particlesto a constant-rate partial drying treatment by continuous contact withsaid drying gas at a temperature of about 200 F. during a time intervalof about 12 minutes.

3. A process as defined in claim 1, wherein said treatment is carriedout in separate superimposed confined zones while said particles aregravitating as a continuous compact moving stream whose rate of flow iscontrolled at the point of discharge from the lower confined zone, andwherein said lower zone is adjustable as to volume, whereby the flowrate of said particles may be set to provide a desired residence time inthe upper zone and the volume of the lower zone adjusted to providetherein the necessary residence time for the particles to complete thedesired aging.

4. A process as defined in claim 3, wherein said lower zone is heated byindirect heat exchange to maintain the particles passing therethroughsubstantially at the temperature iat which they were discharged fromsaid upper zone.

References Cited in the le of this patent UNITED STATES PATENTS1,762,228 Holmes e June 10, 1930 2,509,014 Payne et al May 23, 19502,558,206 Baird June 26, 1951

1. IN A CONTINUOUS PROCESS FOR TREATING PREFORMED PARTICLES OFSILICA-ALUMINA HYDROGEL HAVING A MOISTURE CONTENT UP TO ABOUT 300% BYWEIGHT TO CONDITION THE SAME FOR USE AS A CONTACT MATERIAL, THEIMPROVEMENT WHICH COMPRISES INTRODUCING THE WET HYDROGEL PARTICLES INTOA FLOWING STREAM OF DRYING GAS HAVING A TEMPERATURE OF ABOUT 150* TO200* F. FOR A TIME SUFFICIENT TO REDUCE THE MOISTURE CONTENT OF SAIDPARTICLES TO ABOUT 200%, PASSING THE PARTIALLY DRIED HYDROGEL PARTICLESTHROUGH AN AGING ZONE MAINTAINED TO ABOUT 138* F. DURING A TIME INTERVALOF ABOUT ONE HOUR, AND THEN WASHING AND DRYING THE AGED PARTICLES.